Higgs Signal Research Articles

Current experimental constraints on the lightest Higgs boson mass in the constrained MSSM

We examine the parameter space of the constrained MSSM by considering various experimental constraints. For the dark matter sector, we require the neutralino dark matter to account for the relic density measured by the WMAP and satisfy the XENON limits on its scattering rate with the nucleon. For the collider constraints, we consider all relevant direct and indirect limits from LEP, Tevatron and LHC as well as the muon anomalous magnetic moment. Especially, for the limits from Bs→μ+μ−, we either directly consider its branching ratio with the latest LHC data or alternatively consider the double ratio of the purely leptonic decays defined by Br(Bs→μ+μ−)/Br(Bμ→τντ)Br(Ds→τντ)/Br(D→τμτ). We find that under these constraints, the mass of the lightest Higgs boson (h) in both the CMSSM and the NUHM2 is upper bounded by about 124 GeV (126 GeV) before (after) considering its theoretical uncertainty. We also find that for these models the di-photon Higgs signal at the LHC is suppressed relative to the SM prediction, and that the lower bound of the top-squark mass goes up with mh, reaching 600 GeV for mh=124 GeV.

The constrained NMSSM and Higgs near 125 GeV

We assess the extent to which various constrained versions of the NMSSM are able to describe the recent hints of a Higgs signal at the LHC corresponding to a Higgs mass in the range 123–128 GeV.

Impact of the relatively light fourth family neutrino on the Higgs boson search

The existence of a fourth fermion generation has mostly been considered as a source of enhanced Higgs signals with respect to the 3 family Standard Model predictions. However, a fourth Standard Model family neutrino could cause the opposite situation. It is shown that relatively light fourth family neutrino (2mν4<mH) could drastically change the interpretation of the search results for the Higgs boson, especially if mH<170 GeV.

Interpreting the LHC Higgs search results in the MSSM

Recent results reported by the ATLAS and CMS experiments on the search for a SM-like Higgs boson both show an excess for a Higgs mass near 125 GeV, which is mainly driven by the γγ and ZZ⁎ decay channels, but also receives some support from channels with a lower mass resolution. We discuss the implications of this possible signal within the context of the minimal supersymmetric Standard Model (MSSM), taking into account previous limits from Higgs searches at LEP, the Tevatron and the LHC. The consequences for the remaining MSSM parameter space are investigated. Under the assumption of a Higgs signal we derive new lower bounds on the tree-level parameters of the MSSM Higgs sector. We also discuss briefly an alternative interpretation of the excess in terms of the heavy CP-even Higgs boson, a scenario which is found to be still viable.

Higgs signal gains strength

Higgs signal gains strength

Search for the Higgs portal to a singlet fermionic dark matter at the LHC

We consider a simple extension of the standard model with a singlet fermionic dark matter. Its thermal relic density can be easily accommodated by a real singlet scalar messenger that mixes with the standard model Higgs boson. The model can change significantly the Higgs signals at the LHC via sizable invisible decays of two Higgs-like scalar bosons. After imposing the constraints from the electroweak precision tests, colliders and dark matter search experiments, one concludes that two or one or none of the two Higgs bosons, depending on the mass relations among two scalar bosons and the dark matter fermion and their couplings. In particular, if a standard model Higgs-like scalar boson is discovered around 120--125 GeV region at the LHC, it would be almost impossible to find the second Higgs-like boson since it is mostly a singlet scalar, whether it is heavier or lighter. This model can be further tested by direct dark matter search experiments.

Branching Ratios from &amp;lt;i&amp;gt;H→γγ&amp;lt;/i&amp;gt; and &amp;lt;i&amp;gt;H→Zγ&amp;lt;/i&amp;gt; with a 125 GeV Higgs Boson

Motivated by the recent result reported from LHC on the di-photon search from the Standard Model (SM) Higgs boson, we obtain limits on the anomalous couplings Hγγ and HZγ. We also perform a calculation at tree level of the decay widths as well as of the branching ratios for the reactions H → γγ and H → Zγ in the context of effective lagrangian for Higgs boson masses 115 ≤MH ≤ 130 GeV. We find that the decay widths and branching ratios from these reactions enhanced significantly due to the anomalous Hγγ and HZγ vertex, which would lead to measurable effects in Higgs signals at the LHC. Moreover, our results complement other studies on the channels H → γγ and H → Zγ.

Light NMSSM Higgs bosons in SUSY cascade decays at the LHC

Abstract An interesting feature of the next-to-minimal supersymmetric standard model (NMSSM) is that one or more Higgs bosons may be comparably light ( ${M_{{{H_i}}}} &lt; {M_Z}$ ) without being in conflict with current experimental bounds. Due to a large singlet component, their direct production in standard channels at the Large Hadron Collider (LHC) is suppressed. We demonstrate that there are good prospects for observing such a light Higgs boson in decays of heavy neutralinos and charginos. We consider an example scenario with $20\,GeV &lt; {M_H}_{{_1}} &lt; {M_Z}$ and show that a large fraction of the cascade decays of gluinos and squarks involves the production of at least one Higgs boson. Performing a Monte Carlo analysis at the level of fast detector simulation, it is demonstrated how the Higgs signal can be separated from the main backgrounds, giving access to the Yukawa coupling of the Higgs to bottom quarks. Analyzing the resulting $b\overline b$ mass spectrum could provide an opportunity for light Higgs boson discovery already with 5 fb−1 of LHC data at 7 TeV.

GeV SCALE ASYMMETRIC DARK MATTER FROM MIRROR UNIVERSE: DIRECT DETECTION AND LHC SIGNATURES

Mirror universe is a fundamental way to restore parity symmetry in weak interactions. It naturally provides the lightest mirror nucleon as a unique GeV-scale asymmetric dark matter particle candidate. We conjecture that the mirror parity is respected by the fundamental interaction Lagrangian, and its possible soft breaking arises only from non-interaction terms in the gauge-singlet sector. We realize the spontaneous mirror parity violation by minimizing the vacuum Higgs potential, and derive the corresponding Higgs spectrum. We demonstrate that the common origin of CP violation in the visible and mirror neutrino seesaws can generate the right amount of matter and mirror dark matter via leptogenesis. We analyze the direct detections of GeV-scale mirror dark matter by TEXONO and CDEX experiments. We further study the predicted distinctive Higgs signatures at the LHC.

Standard Model Higgs Combination from CMS with up to 1.7 fb−1of data

The combination is presented of searches for a standard model (SM) Higgs boson in eight decay modes: H->gamma,gamma, H->tau,tau, H->bb, H->WW->2l2nu, H->ZZ->4l, H->ZZ->2l2tau, H->ZZ->2l2nu, and H->ZZ->2l2q. The searches were performed by the CMS Collaboration using 1.1-1.7 fb-1 of integrated luminosity, depending on the analysis. No excess compatible with a SM Higgs signal has been observed; the largest excursion of the observed data from the expected background has a probability of 0.4 after taking into account the look-elsewhere effect. The SM Higgs boson is excluded at 95% C.L. in three mass ranges 145-216, 226-288, and 310-400 GeV/c2, while the expected exclusion range is 130-440 GeV/c2.

A 125 GeV Higgs and Its Diphoton Signal in Different SUSY Models: A Mini Review

In this paper we briefly review our recent studies on a 125 GeV Higgs and its diphoton signal rate in different low-energy supersymmetric models, namely, the minimal supersymmetric standard model (MSSM), the next-to-minimal supersymmetric standard model (NMSSM), the nearly minimal supersymmetric standard model (nMSSM), and the constrained MSSM. Our conclusion is as follows (i) in the allowed parameter space the SM-like Higgs boson can easily be 125 GeV in the MSSM, NMSSM, and nMSSM, while it is hard to realize in the constrained MSSM; (ii) the diphoton Higgs signal rate in the nMSSM and constrained MSSM is suppressed relative to the prediction of the SM, while the signal rate can be enhanced in the MSSM and NMSSM; (iii) the NMSSM may allow for a lighter top squark than the MSSM, which can thus ameliorate the fine-tuning problem.

Higgs portal inflation

The Higgs sector of the Standard Model offers a unique opportunity to probe the hidden sector. The Higgs squared operator is the only dimension two operator which is Lorentz and gauge invariant. It can therefore couple both to scalar curvature and the hidden sector at the dim--4 level. We consider the possibility that a combination of the Higgs and a singlet from the hidden sector plays the role of inflaton, due to their large couplings to gravity. This implies that the quartic couplings satisfy certain constraints which leads to distinct low energy phenomenology, including Higgs signals at the LHC. We also address the unitarity issues and show that our analysis survives the unitarization procedure.

Lightest supersymmetric particle stability and new Higgs signals at the LHC

The fate of R-parity in the context of the minimal supersymmetric standard model is a central issue which has profound implications for particle physics and cosmology. In this article we discuss the possibility of testing the mechanism responsible for the stability of the lightest supersymmetric particle at the Large Hadron Collider (LHC). The simplest theoretical framework where R-parity conservation can be explained dynamically allows for two types of B-L models. In the first scenario the new Higgses decay mainly into two right-handed neutrinos giving rise to exotic lepton number violating signals together with displaced vertices. In the second model one could have peculiar channels with multileptons and/or multiphotons in the final state. In both cases, the local B-L gauge symmetry is broken at the TeV scale and the discovery of the new Higgs bosons may be possible at the LHC. We investigate in detail the production mechanisms for the Higgs bosons relevant for the LHC and the key decays which would shed light on how R-parity is conserved. These results may help to understand the link between the cold dark matter of the universe and the missing energy that could be observed at the LHC if supersymmetry is realized in nature.

Signals ofCPviolation beyond the MSSM in Higgs and flavor physics

We study an extension of the Higgs sector of the minimal supersymmetric standard model (MSSM), considering the effects of new degrees of freedom at the TeV scale and allowing for sources of $CP$ violation beyond the MSSM. We analyze the impact of the beyond-the-MSSM sources of $CP$ violation on the Higgs collider phenomenology and on low energy flavor and $CP$-violating observables. We identify distinct Higgs collider signatures that cannot be realized, either in the case without $CP$-violating phases or in the $CP$-violating MSSM, and investigate the prospects to probe them at the Tevatron and the LHC. The most striking benchmark scenario has three neutral Higgs bosons that all decay dominantly into $W$ boson pairs and that are well within the reach of the 7 TeV LHC run. On the other hand, we also present scenarios with three Higgs bosons that have masses ${M}_{{H}_{i}}\ensuremath{\gtrsim}150\text{ }\text{ }\mathrm{GeV}$ and decay dominantly into $b\overline{b}$. Such scenarios are much more challenging to probe and can even lie completely outside the reach of the 7 TeV LHC run. We explore complementary scenarios with standard MSSM Higgs signals that allow us to accommodate a nonstandard ${B}_{s}$ mixing phase as indicated by D0, as well as the excess in ${B}_{s}\ensuremath{\rightarrow}{\ensuremath{\mu}}^{+}{\ensuremath{\mu}}^{\ensuremath{-}}$ candidates recently reported by CDF. We find that, in contrast to the MSSM, a minimal flavor-violating soft sector is sufficient to generate significant corrections to $CP$-violating observables in meson mixing, compatible with Electric Dipole Moment constraints. In particular, a ${B}_{s}$ mixing phase ${S}_{\ensuremath{\psi}\ensuremath{\phi}}\ensuremath{\lesssim}0.15$ can be achieved for specific regions of parameter space, compatible with all the presently available experimental constraints on flavor observables. Such a nonstandard ${B}_{s}$ mixing phase would unambiguously imply a sizable suppression of ${S}_{\ensuremath{\psi}{K}_{S}}$ with respect to the standard model prediction and a $\mathrm{BR}({B}_{s}\ensuremath{\rightarrow}{\ensuremath{\mu}}^{+}{\ensuremath{\mu}}^{\ensuremath{-}})$ close to its 95% C.L. upper bound of $1.1\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}8}$.

Implications of the stability and triviality bounds on the standard model with three and four chiral generations

We revisit the stability and triviality bounds on the Higgs boson mass in the context of the Standard Model with three and four generations (SM3 and SM4, respectively). In light of the recent results from LHC the triviality bound in the SM3 has now become obsolete, and the stability bound implies for a Higgs mass of e.g. mH=115 GeV the onset of new physics before 650 TeV, whereas there are no limits for mH>133 GeV. For the SM4, the stability and triviality curves intersect and bound a finite region. As a consequence, the fourth generation fermions place stringent theoretical limits on the Higgs mass, and there is a maximal scale beyond which the theory cannot be perturbatively valid. We find that the Higgs mass cannot exceed 700 GeV for any values of the fourth generation fermion masses. Turning the argument around, the absence of a Higgs signal for mH<600 GeV excludes a fourth generation with quark masses below 300 GeV and lepton masses below 350 GeV. In particular, the quark bounds also hold for the small mixing scenarios for which the direct limits from Tevatron and LHC are not applicable, and the lepton bounds we obtain are stronger than the collider limits. If a Higgs boson lighter than 700 GeV is not observed, a fourth generation of chiral fermions with perturbative Yukawa couplings will be conclusively excluded for the full range of parameters.

Model-independent Higgs coupling measurements at the LHC using theH→ZZ→4ℓlineshape

We show that combining a direct measurement of the Higgs total width from the $H\ensuremath{\rightarrow}ZZ\ensuremath{\rightarrow}4\ensuremath{\ell}$ lineshape with Higgs signal rate measurements allows Higgs couplings to be extracted in a model-independent way from CERN LHC data. Using existing experimental studies with $30\text{ }\text{ }{\mathrm{fb}}^{\ensuremath{-}1}$ at one detector of the 14 TeV LHC, we show that the couplings squared of a 190 GeV Higgs to $WW$, $ZZ$, and $gg$ can be extracted with statistical precisions of about 10%, and a 95% confidence level upper limit on an unobserved component of the Higgs decay width of about 22% of the standard model Higgs width can be set. The method can also be applied for heavier Higgs masses.

Gluon-gluon contributions to W + W − production and Higgs interference effects

In this paper we complete our re-assessment of the production of W boson pairs at the LHC, by calculating analytic results for the gg -> W+ W- -> (\nu l l\nu) process including the effect of massive quarks circulating in the loop. Together with the one-loop amplitudes containing the first two generations of massless quarks propagating in the loop, these diagrams can give a significant contribution with a large flux of gluons. One of the component parts of this calculation is the production of a standard model Higgs boson, gg -> H and its subsequent decay, H -> W+(-> \nu l) W-(-> l \nu). We will quantify the importance of the interference between the Higgs boson production process and the gluon-induced continuum production in the context of searches for the Higgs boson at the Tevatron and the LHC. For instance, for mH < 140 GeV the effect of the interference typically results in around a 10% reduction in the expected number of Higgs signal events. The majority of this interference is due to non-resonant contributions. Therefore cuts on the transverse mass such as those currently used by the ATLAS collaboration reduce the destructive interference to about a 1% effect. We advocate that a cut on the maximum transverse mass be used in future Higgs searches in this channel.

Higgs signal sinks from view

Higgs signal sinks from view

Higgs signal sinks from view

Higgs signal sinks from view

Di-photon Higgs signal at the LHC: A comparative study in different supersymmetric models

As the most important discovery channel for a light Higgs boson at the LHC, the di-photon signal gg→h→γγ is sensitive to underlying physics. In this work we investigate such a signal in a comparative way by considering three different supersymmetric models, namely the minimal supersymmetric standard model (MSSM), the next-to-minimal supersymmetric standard model (NMSSM) and the nearly minimal supersymmetric standard model (nMSSM). Under the current collider and cosmological constraints we scan over the parameter space and obtain the following observation in the allowed parameter space: (i) In the nMSSM the signal rate is always suppressed; (ii) In the MSSM the signal rate is suppressed in most cases, but in a tiny corner of the parameter space it can be enhanced (maximally by a factor of 2); (iii) In the NMSSM the signal rate can be enhanced or suppressed depending on the parameter space, and the enhancement factor can be as large as 7.